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磷, NOx. 安 排. 预习时: 清洗实验 2.11 磷测定 ( 快速消解法 ) 所需器皿。 采集实验 3.2 大气 NOx 样品,清洗 3.2 所需器皿。 考虑 2 周后的自主实验。 实验: 上午,磷的测定,考试实验。 下午,测定大气 NOx 。. 2.11. Determination of Orthophosphates. Purpose:

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Presentation Transcript
slide2
安 排

预习时:

  • 清洗实验2.11磷测定(快速消解法)所需器皿。
  • 采集实验3.2大气NOx样品,清洗3.2所需器皿。
  • 考虑2周后的自主实验。

实验:

  • 上午,磷的测定,考试实验。
  • 下午,测定大气NOx。
2 11 determination of orthophosphates
2.11. Determination of Orthophosphates

Purpose:

  • To understand the principles of determination of orthophosphate, and to master one of the sample pretreatment methods, oxidative digestion.
  • To get familiar with the operation of UV-Vis spectrophotometer.
slide4

Sample

Filter (through 0.45μm membrane)

Digestion

Total phosphorus

Residue

Solution

Digestion

  • Dissolved Orthophosphate

Dissolved Total Phosphorus

slide5
Samples:
  • Diluted organophosphorous pesticide waste water
  • One blank and one sample for each student.
method principle
Method principle
  • Phosphoantimonylmolybdenum blue method
  • Maximum absorbance wavelength at 700-900 nm.
  • Calibration curve for quantification.
  • Digestion to get total phosphates.
procedure
Procedure

1. Digestion

diluted waste water + oxidizing reagent

160℃ for 15min

2. Color development

transferring, adding reagents, preparing calibration curve

3. Detection

700 nm, water as the reference

questions
Questions
  • Should the solutions of the calibration curve be digested as the samples? And why?
  • Yes.
  • Do we need to add the color developing reagents accurately?
  • Yes.
3 2 determination of nitrogen oxides nox
3.2. Determination of Nitrogen Oxides (NOx)

Purpose:

  • To understand the principle of determination of NOx,
  • and to grasp the method of NOx determination and the use of spectrophotometer;
  • as well as to master one of the air sampling methods, solution absorption.
method principle1
Method principle
  • NO2 in the air is dissolved in the absorbing solution and forms nitrous acid.
  • Nitrous acid reacts with sulfanilic acid, then couples with N-(1-naphthyl)-ethylenediamine dihydrochloride and forms rose-colored azo dye.
  • The determination of azo dye is carried out at 540 nm.
slide11

Air

CrO3

Drying

Pump

Waste

Bottle

Soln

NOx = NO + NO2 + N2O

production of nox in the lab
Production of NOx in the lab

3 Cu + 8 HNO3(diluted) =

3 Cu(NO3)2 + 2 NO + 4 H2O

Cu + HNO3 = Cu(NO3)2 + 2 NO2 + 2 H2O

4 HNO3 + (heat) = 4 NO2 + 2 H2O + O2

procedure1
Procedure
  • Collect the sample

2. Prepare the calibration curve

3. Detection at 540 nm

additional questions
Additional Questions
  • What are the possible factors to cause the method blank?
  • Is the NOx level you determined within the normal range?
calculation
calculation
  • NOx (μg/m3) =

Calibration curve: Y = bX + a

Here,

Bs = 1/b; A0 = a

slide16
什么是空白

包括现场空白、仪器空白和方法空白。以水样为例。

  • 现场空白:在采样现场带上纯水。经历与其他样品相同的采集、储存、运输、分析全过程。
  • 仪器空白(溶剂空白):不含目标物的水或溶剂为样品,经历仪器分析的全过程。
  • 方法空白(样品制备空白) :不含目标物的水或溶剂为样品,经历样品预处理和仪器分析的全过程。
slide17
空白值只能说明是否玷污,不能说明玷污有多少。空白值只能说明是否玷污,不能说明玷污有多少。

测定结果能不能扣除空白?

  • 如果用的是工作曲线法,分光光度测定中可以扣除空白。
  • 如果是单点测定,一般不宜扣除空白。除非测定20次,且偏差在允许范围内。
  • Excel“趋势线格式”中选择截距不为零。
slide18
空白
  • 空白值指试剂经过同样的样品处理后的吸光值,即被测物浓度为零的样品吸光值。
  • 空白有化学意义,用于检验试剂的纯度和样品处理过程的玷污程度。
  • 报告数据时必须报告空白值。

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slide19
工作曲线是否可以过原点?
  • 试剂在工作曲线的其他点的溶液中同样存在,量也一样,处理过程一样,因此空白应当成为工作曲线上的一个点。空白所在的点不等于原点。没有理由要求工作曲线通过每一个点。

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slide20
可以在样品测值中扣除空白的吸光值,即使工作曲线平移。但工作曲线不应强求过原点。可以在样品测值中扣除空白的吸光值,即使工作曲线平移。但工作曲线不应强求过原点。
  • 如果以空白做参比,则无法得知试剂的污染程度。即使以空白做参比,工作曲线仍然不应强求过原点。

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